1. Field of the Invention
The present invention relates to a developer for developing an electrical latent image in electrophotography and electrostatic printing, and more particularly to a non-magnetic mono-component developer.
2. Description of the Prior Art
Generally, a two-component developing system and a mono-component developing system are known for developing apparatuses. From the standpoints of prevention of deterioration of chargeabiity and size reduction of an image-forming apparatus, the mono-component developing system has often been employed.
The mono-component developing system is classified into a magnetic mono-component system and a non-magnetic mono-component system. The magnetic mono-component developing system usually requires addition of black magnetic powder to the toner. Therefore, the non-magnetic mono-component developing system can be advantageously employed in a full-color image-forming apparatus. In the non-magnetic mono-component developing system, a developer-regulating member is disposed so as to contact against a developer-supporting member to permit the non-magnetic mono-component developer to pass through a clearance between the developer supporting ember and the developer-regulating member, so that a toner thin layer is formed on the supporting member and the toner is electrically charged at the same time. The thin layer of the charged toner is transported as it is to a developing region in which the electrostatic latent image formed on an electrostatic latent image-support member is developed by the toner.
Generally, a toner is added with inorganic fine particles (externally) as a fluidizing agent, such as silica and titania. For example, Japanese Patent Laid-Open Application No. Hei 7-43930 discloses a non-magnetic mono-component toner which is externally added with a hydrophobic silica and a hydrophobic titanium oxide having a mean particle size of 0.02 to 0.5 .mu.m, a hydrophobicity of 20 to 95%, and an optical transmission of not less than 40% at 400 nm. In the mono-component developing system, however, because toner particles are forced to pass through the clearance (regulating portion) between the developer-supporting member and the developer-regulating member so as to be electrically charged, some stress is exerted upon the toner particles in the electrical charging process. With the technique described in the above cited publication, it is difficult to satisfactorily solve the problem of deterioration of fluidity which will occur when the toner is repeatedly used. Another problem is that as the fluidizing agent is buried in the toner surface, the surface conditions of the toner will change, it being thus difficult to maintain stably the properties of the toner.